Print element actuating mechanism



s- 5, 1958 J. E. HICKERSQN 2,846,043

' PRINT ELEMENT ACTUATING MECHANISM Filed Dec. 27, 1955 2 Sheets-Sheet 1 FIG.

INVENTOR JOHN E. HICKERSON (\l AGENT United States Patent PRINT ELEMENT ACTUATING MECHANISM John E. Hickerson, Wappingers Falls, N. Y., assignor to International Business Machines Corporation, New York, N. Y., a corporation of New York Application December 27, 1955, Serial No. 555,452 Claims. (Cl. 197-55) This invention relates to typewriting machines of the mechanical class and more particularly to the mechanisms thereof by which a manual key operation is effective to impel a selected type character against a print record to effect printing, and by which the selected type character is restored subsequent to printing. The invention is embodied for purposes of description in a typewriter having a single element type carrier in which the carrier is simultaneously rotated and moved longitudinally to bring the selected character to print position aligned with a print platen.

In the conventional all mechanical typewriter, the manual depression of a type key is effective through associated connective linkage to impel a corresponding type element against a printing platen and intervening inked ribbon and print sheet, the actual printing force with which the type element strikes the platen being proportional to the force with which the type key was depressed. It is thus evident that the impression of a series of typed characters is consistent only to the extent that the operator is capable of applying equal pressure to each of the associated type keys, as operated, assuming, of course, that an equal key pressure is equally effective through each key associated connective mechanism, the latter condition, in itself being difiicult to obtain.

An attendant characteristic of the conventional all mechanical typewriter is that as long as an actuated key is held in its depressed position, the corresponding type element, through the associated connective linkage, maintains the related type element visibly obstructing the print position of the record on which that element printed. In addition, it is evident that the operator must release the depressed key to permit it to restore clear of the print position before the next desired type element strikes the platen; otherwise, jamming of the type elements will result.

It is accordingly, an object of the subject invention to provide an improved typewriter wherein the printing force with which type characters engage a print record, is equal and independent of the force with which the associated type keys are depressed.

It is a further object to provide an improved typewriter wherein the travel of any of a plurality of type keys as depressed, not only selects the corresponding type character for printing, but also acts through a single linkage common to all the type keys to first cock an impeller mechanism, and then release the impeller to force the selected type character against a print record and backing platen, the printing energy of the impeller being accordingly equal regardless of any differences in the force applied to the type keys as depressed.

A still further object of the invention is to provide an improved typewriter wherein any selected type character after printing engagement with a print record, immediately restores clear of the print position even though the related type key whose depression initiated the printing, is still in a depressed position.

Other objects of the invention will be pointed out in the following description and claims and illustrated in the accompanying drawings, which disclose, by way of example, the principle of the invention and the best mode, which has been contemplated, of applying that principle. 5

In the drawings:

Fig. 1 is an exploded perspective view of a representative type key, a common impeller or print element actuating mechanism, a single element type carrier, and various associated connective mechanism.

Fig. 2 is a left end view of the impeller for the single element type carrier, various parts being broken away to facilitate illustration, the impeller being shown in its uncocked position and the representative type key being shown in its normal position.

Fig. 3 is a view similar to Fig. 1 but shows the impeller as fully cocked and about to be knocked off as a result of a depression of the representative type key.

Fig. 4 is a view similar to Fig. 2 butshows the common impeller after being released or knocked 011, the representative type key being shown in its maximum depressed position.

Referring now to Fig. 1, the inventive mechanism is shown as applied to a simplifiediepresentation of a typewriter structure, only those parts necessary to illustrate the cooperation of the inventive mechanism with the other typewriter elements being shown. In the simplified typewriter represented, only a single type key 10 is shown although in an actual typewriter one key for each of the possible type characters would, of course, be provided.

The structure comprises a prism shaped, single element type carrier 11 on the faces of which all desired type characters are embossed in column by column and side by side alignment as indicated. The type carrier is secured to a shaft 12 which is rotatably supported on one end of a type carrier support member 13, the member 13 being pivotally supported at its other end on extending portions of a bushing 14 carried by a reciprocable carriage 15. The carrier support 13, in addition to being rotatable about the bushing 14, is adapted to be advanced in increments from the left to the right in Fig. 1 by an equivalent motion of the carriage 15 and bushing 14. This permits the type carrier 11 to be presented to suecessive print positions of a line of a stationary print sheet 16 which is arranged between the carrier 11 and a platen 17.

As the type carrier is advanced, print position by print position, the platen 17, which has a face equal in width and height to that of any one of the type characters of the type carrier 11, is advanced in synchronism therewith a manner such as fully described in patent application Serial Number 322,04-5 filed January 19, 1953, now Patent No. 2,757,775.

As the type carrier 11 and platen 17 advance into a print position, the normal alignment therebetween is such that a home print character is aligned with the platen. Thereafter, dependent upon the particular type key 10 depressed, the type carrier 11 is rotated as required, and also shifted further to the right, it required, to bring the related type character in alignment with the platen. The printing action is then completed by a clockwise rocking of the support 13 on the bushing 14 which forces the selected type carrier against the platen 17 and an intervening inked ribbon 18 and the print sheet 16. p

The horizontal movement of the type carrier 11 both for the print position by print position advance thereof, and also for the horizontal type character selection motion within a print position, is applied through the previously mentioned carriage member 15 which is slid- Patented' Aug. 5, 1958' ably mounted on a shaft 19, the latter being supported at its ends by a left end frame 20, and a similar right end frame (not shown), the end frames being rigidly secured to a suitable base plate 21. The carriage extends forward through and beyond legs 13A and 13B of the type carrier support 13 and carries a roller 15A on its forward end which engages a guide track 26, also supported at its ends by the end frames. Slidably extending through the center of the previously mentioned bushing 14 secured to the carriage 15 is a bar member 22 which is rotatably supported at its ends by the end frames, The purpose of bar 22 will be later explained. It is evident that as the carriage 15 moves towards the right in Fig. 1, it bears against the leg 13A and carries the support 13 and carrier 11 therewith. Similarly, if the carriage moves toward the left in Fig. 1, it bears against the leg 13B and carries the support 13 and carrier 11 therewith. The manner in which the carriage 15 may be advanced print position by print position to succeeding print positions of a line of the print sheet, and shifted 1 to columns to the right when in each print position as determined by the type character key depressed, is fully described in the above mentioned application Serial Number 332,045.

There is also described in the same application, the manner in which the depression of each type key also effects a proper type character selection rotation of the bar 22, this rotation being applied through a tape 23 operatively linking a pulley 24 secured to the carrier shaft 12 and a pulley 25 mounted on the bar 22 for rotation therewith, to position the desired type character in printing position. Although the pulley 25 is fixed to the bar 22 for angular motion therewith, it is slidable longitudinally with the support 13 on the bar 22. After the last character is printed on a print line, the carriage is returned in a well known manner and the print sheet advanced one or more lines as required to bring the next desired print line into print position. The description up to this point has been directed to a representative typewriter structure to which the subject inventive mechanism, to be described immediately hereinafter, may be applied.

Referring now to Figs. 1 and 2, each typekey such as 10 is secured to the-one end of a key lever 27 which is pivotally supported at its other end on pivot 28 carried by frame 20, the key lever 27 extending through a vertically extending guide slot in a related guide member 29 also secured to frame 20. A 3 armed crank 30 is pivoted at 31 on the frame 20, and is biased counterclockwise in Fig. 2 by a spring 33 connected between an arm 30A thereof and fixed stud 34, to maintain a bail rod 35 carried on the second arm 30B of the lever 30 in engagement with a surface 27A of the key lever 27. The key lever 27 and associated key 10 are accordingly maintained in a normal upward position as indicated in Fig. 2 with the top of the lever engaging the top of the slot in, the guide 29. It will be appreciated that in a complete typewriter mechanism, the bail rod 35 extends under and is engaged by all the type key levers thereof.

Upon a depression of a type key, such as key 10, the resultant clockwise rocking of the associated key lever 27 is effective to apply a rotational and longitudinal selection motion to the type element 11 to position the related type character thereof in the print position. In addition, the clockwise rocking of the lever 27 is effective through the surface 27A thereof and bail rod 35 to rock the 3 armed crank 30 clockwise in Fig. 2. This rocking of crank 30 is, in turn, effective through a link 36 connecting the third arm 30C of crank 30' and an arm 38A of a rocker 38, to rock the latter clockwise on a shaft 39, the shaft 39 being secured to and extending outwardly from the frame 20.

Pivotally mounted on a second arm 38B of rocker 38 is a pawl 40. A spring 41 extending between the pawl and the arm 38A of rocker 38, tensions the pawl clockwise in Figs. 2 and 3 relative to the arm 38B of rocker 38, so as to maintain a latch surface 40A thereof engaged with a mating latch arm 44A of a cocking lever 44, the latter being pivotally mounted on the shaft 39. The cocking lever 44 is tensioned counterclockwise on shaft 39 so as to normally maintain the latch arm 44A engaged with the latch surface 40A of pawl 40, by a spring 45 connected from another arm 44B of cooking lever 44 to one arm 46A of a 3 armed bail lever 46. The bail lever 46 is secured to a bail shaft 47 which, in turn, is pivotally supported by the left end frame 20 and corresponding right end frame (not shown). The bail lever 46 and associated bail shaft 47 are normally blocked against rotation in a clockwise direction from the position indicated in Fig. 2 by the engagement of a latch arm 48A of a latch member 48 with a second arm 46B of lever 46. The latch member 48 is pivotally mounted on shaft 39 and is tensioned counterclockwise in Fig. 2 by a spring 50 connected from another arm 48B thereof to a fixed stud 51, so as to normally maintain the arms 48A and 46B engaged and the bail lever 46 accordingly latched against clockwise rotation.

By reason of the above described linkages between the various structural elements, the clock-wise rotation of the 3 armed rocker 38 as a result of a depression of a key 10 is effective through associated pawl 40 to rock the cocking lever 44 clockwise on shaft 39, thus stretching the spring 45 of'the latched bail lever 46 from the position indicated in Fig. 2, to a position as indicated in Fig. 3. The cocking lever 44 includes a slot 44C in which is arranged a pin 52, the pin being secured to the cocking lever by hex nut 52A. The pin 52 extends laterally beyond the lever 44 and into the plane of the arm 48A of latch 48. By loosening nut 52A, the pin 52 may be adjusted in the slot 44A to give accurate control of the amount of rocking of cocking lever 44 required to engage pin 52 with the latch member 48. As the cocking lever 44 rotates towards the position indicated in Fig. 3, the pin 52 accordingly engages the under surface of the arm 48A and displaces the latch member 48 clockwise on the shaft 39. It will be noted in Fig. 3 that the latch 48 has been displaced by the rocking of the cocking lever 44 so that the latch surface of arm 48A is just about to be moved clear of the arm 46A of bail lever 46.

Referring now to Fig. 1, it will be noted that secured to bail shaft 47 for movement therewith is a ball 53 which is operationally engaged by the nose 54A of a follower 54, the latter being secured to the outer surface of the leg 13A of the type carrier support 13. A spring 56 linked between the follower 54 and fixed structure tensions the follower 54 and associated support 13 in a counterclockwise direction relative to the bushing 14 in Fig. 1, so as to maintain the nose 54A of the follower engaged with the bail 53 on the shaft 47. Thus when the lever 46 and associated shaft 47 and the bail 53 are in the positions indicated in Figs. 1, 2 and 3, the type carrier support 13 is. angularly positioned on the carriage bushing 14 so that the type carrier 11 is clear of the print sheet 16.

With a slight further downward motion of the key 10 from the position indicated in Fig. 3, the resultant further rocking of arm 38 and lever 44 moves the latch arm 48A clear of the arm 46B of bail lever 46, thus freeing the lever 46 and associated bail shaft 47 for rapid counterclockwise rotation under the urging of associated stretched spring 45, from the position indicated in Fig. 3, to the position indicated in Fig. 4. This rapid rotation of the shaft 47' is effective through the bail 53 and follower 54, to rapidly rock the support 13 and associated type carrier 11 clockwise (in Fig. l) on bushing 14 so as to forcibly engage theselected type character with the ribbon 18, print record 16 and backingplaten 17 to effect the character.

Referring now to Fig. 4, it will be noted that after the bail lever 46 is released and after it rotates clockwise on shaft 47 sufficiently to effect the print operation, a third arm 46C thereof engages the nose 40B of the pawl 40 and displaces it counterclockwise on its supporting arm 38B of rocker 38 so as to disengage the latch surface 40A of pawl 40 from the mating latch surface of arm 44A of cocking lever 44. The lever 44 is accordingly freed for rocking in a counterclockwise direction on shaft 39 until it engages a stop pin 55 carried by the end frame 16, the rocking being effective through arm 44B of lever 44 to further release the tension of spring 45. As the lever arm 44A approaches the pin 55, the tension of the spring 45 has been released to such an extent by the action of both the clockwise rotation of bail lever 46 and the counterclockwise rotation of cocking lever 44, that the tension of spring 56 (see Fig. 1) with the type carrier against the print record 17, is such as to overcome the tension of spring 45. The tension of spring 56 is accordingly effective through follower 54 and type carrier support 13 to rock the type carrier 11 clear of the print position and into the restored position as indicated in Fig. l. The spring 56 is also effective at the same time through follower 54 to rock the bail 53 and associated shaft 47 counterclockwise from the position indicated in Fig. 4 to the position indicated in Fig. 2, so that the arm 48A of latch 48 again drops behind arm 46B of bail 46 as indicated in Fig. 2. By the above action, it is thus evident that even though the operator is still holding the key such as depressed, the type carrier 11 is immediately restored clear of the print sheet after the actual print operation.

With the ball lever 46 again latched, as described above, the release of the key by the operator, permits the key to be restored upward by bail spring 33 acting through crank 3% and associated bail rod 35, from the position indicated in Fig. 4, to the position indicated in Fig. l. The counterclockwise rocking of the crank 30 as it restores from the position of Fig. 4, is effective through the link 36 and rocker 38, to again engage the pawl 40 with the mating arm 44A of cocking lever 44, as indicated in Fig. 2, so that the entire mechanism is now in condition for the next key operation.

It will be appreciated that the subject inventive mechanism although shown as applied to a single type element typewriter, could be readily applied to the conventional mechanical typewriter having a plurality of individual type elements to give the same improved operation wherein the printing impression of each type element would be independent of the actual pressure with which the associated key is depressed, and also, any actuated type element would restore clear of the print record after the print operation even though the related key is held depressed. In such an application, the depression of a type key could be effective to hook or operationally engage the related type element with a common actuating mechanism. The depression of the type key could also be effective through a bail common to all keys, to cock the common actuating mechanism a fixed amount and then release it, the actuating mechanism, accordingly, impelling the particular type element engaged therewith against the print sheet. The operation of the actuating mechanism would also be effective in the same manner as described in the representation shown, to reset itself and also permit the actuated type element to be immediately restored clear of the print position, even though the associated type key is still being held depressed by the operator.

While there have been shown and described and pointed out the fundamental novel features of the invention as applied to a preferred embodiment, it will be understood printing of the selected print 6 that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

1. In a typewriting mechanism having a single print element with a plurality of type characters arranged thereon, a platen having a face area equal to the area assigned to any one of the type characters of said print element, a plurality of key control mechanisms, one for each of the type characters of said element, each adapted when manually displaced to apply a proper type character selection motion to said print element so as to position the element with the corresponding type character aligned with said platen, and a print arm supporting said element on one end of said arm, said arm being pivoted at its other end and adapted to be rocked between a normal position wherein said print element is free of said platen to a position wherein it is engaged with said platen to effect a printing of the particular type character thereof aligned with said platen; apparatus for operating said print arm comprising, in combination, a pivotally supported bail shaft, a bail secured thereto, a bail lever secured to said shaft, a follower secured to said print arm, said follower including a nose portion, spring means acting on said follower to maintain said nose portion thereof in continuous engagement with said bail, a bail rod including yieldable means, said bail rod being common to all of said key control mechanisms and displaceable against the action of said yieldable means upon a manual depression of any one of said key controlled mechanisms, a pivoted rocker arm including a spring tensioned pawl pivotally supported thereon, a pivoted cocking lever normally operationally engaged with said rocker arm for pivoted motion therewith through said pawl, impelling spring means extending between said cocking lever and bail lever, a pivoted latch including spring tensioning means to normally maintain it latchably engaged with said bail lever thus latching the latter against the action of said impelling spring means, connective linkage interconnecting said rocker arm and said bail rod whereby displacement of the latter by a key depression is effective through said rocker arm, pawl and cocking lever to stretch said impelling spring means, and release means secured to said cocking lever for disengaging said latch from said bail lever after a predetermined stretching of said impelling spring means, said bail lever being accordingly free for rapid rocking under the impetus of said stretched spring, said rocking being effective through said bail shaft, bail, follower, and print arm, to forcibly engage said print element with said platen.

2. Apparatus as in claim 1, further characterized in that said bail lever includes a finger extending into the plane of said rocker arm pawl and adapted to engage it during the rapid rocking of said bail lever and as the print element approaches said platen to effect the print operation, the engagement of the finger with the pawl pivoting said pawl onthe associated rocker arm so as to disengage the pawl from said cocking lever, said cocking lever being accordingly free to pivot relative to said rocker arm to further release the tension of the related impelling spring, stationary abutment means for subsequently arresting said cocking lever after a predetermined rocking thereof suflicient to release the tension of the impelling spring means to a point that the follower spring means can override it, the follower spring means accordingly rocking said follower and associated print arm to restore the print element clear of the platen after the printing action, this restoration through said bail and bail shaft restoring said bail lever so that it relatches' on said latch.

3. Apparatus as in claim 2 further characterized by a'first fixed stop for limiting the amount that any of said 7 keycontrol mechanismsimay be manually depressed, and a. second fixed stop for limiting the amountthat said :yieldable means ,actingonsaid bailrod may restore the latter and said depressed key control mechanism upon a -release of the latter, the restoration of the bail rod being effective through said vconnectivelinkage to rock said rocker arm relative to said arrested cocking lever so as toreengage saidassociated pawl Withsaid cocking lever.

4. In a printing mechanism havinga plurality ofprint character elements vand a plurality of key mechanisms, onefor' each of said characters and wherein a key depression selects the related print character forprinting, a common actuating mechanism for applying an equal and fixed printing force to each character as selected comprising,-in combination, a rockable print bail, a bail lever secured tosaid print bail, ,a pivoted cocking lever, spring tensioning means extending between said cocking lever and said baillever, latching means normally operationally engaged with said baililever to prevent a rocking thereof under the urging of saidassociated springtensioning means, a bail mechanism common to all of said key mechanisms and operationally linked to said cocking lever, said bail mechanism being responsive to a depression of any one of said :key mechanisms to pivot said cocking lever from a normal first position to a second fully cocked position to furthertension said spring tensioning means, said cocking lever including means for releasing said latching means after said cocking lever is fully cocked, the tension of said spring tensioning means being accordingly effective to rapidly rock said bail lever and associated print bail, and means for applying the rapid rocking action of said print bail to the selected type character to effect a printing action thereof.

,5. Ina printing mechanism having a plurality of print character elements and a pluralityof key mechanisms, one for each of said character elements and wherein a manual key depression selects the related print character for printing, a common actuating mechanism for effecting a printingaction of each character as selected, comprising, in combination, a rockable print bail, a bail lever secured to said; print bail, a pivoted cocking lever, spring tensioning means extending between said cocking lever and said bail lever, latching mechanism including yieldable meansacting thereon and servingto maintain the latching mechanism normally latchably engaged with said bail lever to prevent arocking thereof under the urging of said associated spring tensioning means, a yieldable bail mechanism common to all of said key mechanisms, linkage, connecting said bail mechanism and cooking lever, a-depression of any one of said key mechanisms being effective through said bail mechanism and said linkage to pivot said cocking lever from a normal first position to a second fully cocked position to further tension said spring tensioning means, a release device associated with said cocking ,lever and operable as said cocking lever reaches itsfully cocked position to unlatch said bail lever latching mechanismvagainst the action of the associated yieldable means, said bail lever and print bail being accordingly rocked rapidly under the urging of said spring tensioning means, and transmission means for rendering said selected printcharacter responsive to action of said print bail said rapid rocking of said print bail eifecting a printing action of said selectedprint character.

6. Apparatus asin claim further characterized by yieldable means acting on said print bail, said rapid rocking of saidprint bailupon release of said bail lever being efiective against the action of said, print bail yieldable means, a disconnect device associated with said linkage and operable to-break the operative connection between said bail mechanism and said cocking lever, a finger carried 'on said bailiever and adapted to operate said disconnect device duringthe rapid rocking of said bail lever as the printing action is effected, said cocking lever-being accordingly free torestore to saidfirst position, said cockingqleverrestoration. further releasing said, spring tensioning ,means so that said ,yieldable irneans acting on said print bail overrides said spring tensioning means and accordingly restores theprint bail, the associated selected print character just printed, and said 'bail lever so that itis againtlatched by said latching mechanism.

7. Apparatus as in claim 6 further characterized'by means including said yieldable bail mechanism as it restores said-depressed key upon release thereof, for resetting said disconnect device to again operatively link said cocking lever and said yieldable bail mechanism through said linkage.

,8. In a printing machine, an actuating mechanism for effecting a printing action of any one of a plurality of print character elements against a print platen, each print character element being selected for printing by a depression of a relatedkey control mechanism of a plurality of such key control mechanisms, comprising, in combination, a.pivoted lever mechanism, means for operationally linking each print character element as selected by a related key depression to said lever mechanism, spring tensioning means acting on said lever mechanism and urging it in a direction to force a selected print character element against said platen, a latch device normally latching said lever mechanism against the action of said spring tensioning means,.bail mechanism common to all of said key control mechanisms and operable upon a depression of any one of said key mechanisms to act on said spring tensioning means to increase the tension thereof, means responsive to said bail mechanism after the increase of tension of said spring tensioning means to unlatch said latch device, said lever mechanism being accordingly rapidly pivoted by said spring tensioning means to impel the selected print character element against said platen, restoring mechanism actuated by said lever mechanism as it pivots to effect said printing action to rapidly restore said lever mechanism and associated selected print character element immediately after the printing action, and yieldablemeans acting on said latch device and operating to relatch said lever mechanism when restored.

9. In a printing machine, an actuating mechanism for effecting a printing action between any selected one of a plurality of type character elements and a platen, each type character element being selectable for printing by a manual depression of a related key control mechanism of a plurality of such mechanisms, comprising, in combination, a rockable member, spring tensioning means acting on said rockable member, a latching device normally preventing said member from rocking under the urging of said spring tensioning means, bail mechanism'common to all of said key control mechanisms and operable upon a depression of anyone of said key mechanisms to increase the tension of said spring tensioning means a fixed amount, means controlled by said bail mechanism after the increase of tension of said spring means to unlatch said rockable member latching device, said member being accordingly freed for rapid rocking by said spring tensioning means, means responsive to said rocking of said rockablemember for effecting a printing action between said platenand the type character element selected by thevkey mechanism depression, and restoring mechanism actuated by said rockable member as it rocks in effecting saidprinting action, to immediately restore said selected type character element to a non-print relationship after said printing action, said restoring mechanism also acting to relatch said rockable member on saidlatching device.

.10. Ina printing machine, an actuating mechanism for effecting a printing action between any selected one of a plurality of type character elements and a platen, each type character element being selectable for printing by a'manual depression of a related key control mechanism of a plurality of such mechanisms, comprising, in combination, a rockable member, spring-tensioning means actingon'said rockable member, a latching device normally preventing said member from rocking under the urging of saidspring tensioning means, bail mechanism. common to all of said key control mechanisms and including a transmission link, said transmission link having an operative and inoperative position, said bail mechanism being operable upon a depression of any one of said key mechanisms to increase the tension of said spring tensioning means a fixed amount through said transmission link in an operative position, means controlled by said ball mechanism through said operative transmission link and after the increase of tension of said spring means to unlatch said rockable member latching device, said member being accordingly freed for rapid rocking by said spring tensioning means, translating mechanism responsive to said rocking of said rockable member for effecting a printing action between said platen and the type character element selected by the key mechanism depression, means actuated by said rockable member as it rocks, to render said transmission link inoperative after the printing action, restoring mechanism also actuated by said rockable member as it rocks in eflecting said print action,

to immediately restore said platen and selected type character element to a non-print relationship after said printing action, said restoring mechanism also acting to relatch said rockable member on said latching device, yieldable means acting on said bail mechanism, said operation of said bail mechanism by said key mechanism depression being efiected against said yieldable means whereby upon a release of said depressed key mechanism said yieldable means restores said bail and key mechanisms, and means responsive to said bail mechanism as it restores to again render said transmission link operative.

References Cited in the file of this patent UNITED STATES PATENTS 966,714 Stallman Aug. 9, 1910 1,008,964 Going et al Nov. 14, 1911 1,150,382 Paulson et a1. Aug. 17, 1915 

